1. Field of the Invention
The present invention relates to an ink jet recording apparatus for performing recording by jetting ink onto a recording medium, and particularly relates to a structure of a waste ink tank for storing waste ink of an ink-jet ink composition containing a pigment, thermoplastic resin, and a dispersing agent in an aqueous medium.
2. Description of the Related Art
Ink jet recording is superior in silence and high-speed printing properties in recording. Further, it has excellent characteristics that the printing process is simple because of direct printing, and printing can be performed with color easily, etc.
In ink jet recording, however, recording is performed by making ink fly from a fine injection nozzle of a recording head. Accordingly, at the injection nozzle portion, ink is often thickened or dried and solidified at the time of non-recording, for example, standby for printing, etc., in printing under an environment of a high temperature and low humidity, or in printing at low frequency, so that there occurs sometimes defective injection or non-injection (loading). Then, injection recovery treatment is carried out to absorb ink from an injection nozzle portion so as to remove ink thickened or dried and solidified at the injection nozzle portion, or injection stability maintaining treatment is carried out to perform flushing periodically to thereby prevent ink from being thickened or dried. The ink generated by the treatment is stored, as waste ink, in a waste ink tank provided in an apparatus. With respect to a waste ink tank, generally, a method is known in which in order to prevent a waste ink from leaking from the waste ink tank during transport or the like, an absorber of porous material is stored in a waste ink tank vessel so that the absorber is impregnated with the waste ink to thereby store and hole the waste ink therein.
Japanese Patent Publication No. Sho. 57-22065 discloses a method in which an absorber is stored and a volatile one of ink components is evaporated by ventilation, heating, or the like. Further, Japanese Patent Publication No. Sho. 60-147344 discloses a method in which a macromolecular absorber is stored to gelate waste ink. According to the method, not only leakage can be prevented but also a larger quantity of ink can be stored than the volume of a waste ink tank to thereby make it possible to reduce the size of the apparatus.
Recently, in an ink jet recording apparatus, on the other hand, such ink is developed in which a pigment is used as coloring material and thermoplastic resin is dispersed and held in a liquid by using a dispersing agent in order to improve the printing speed, the printing quality, and the light and water resistance of printed matters. Such pigment and resin dispersing type ink has advantages in that running or spread of ink is remarkably suppressed and high-level water resistance is obtained by performing heat fixing in recording.
In the case of using such pigment and resin dispersing type ink, in such a conventional configuration of a waste ink tank utilizing an absorber as described above, thickening or solidification of waste ink due to drying is caused on the surfaces of the absorber so as to block the fine holes of the absorber by the waste ink, so that the absorber becomes incapable of absorbing the waste ink. On the other hand, the macromolecular absorber does not absorb a solid component occupying the greater part of the ink composition but holds a water component which is a volatile component, so that its absorbing efficiency is poor. The absorbing efficiency means the ratio of the volume of waste ink capable of being held to the volume of the waste ink tank. Therefore, there has been a problem that the absorber cannot exhibit its ability effectively both in the absorbing speed and absorbing efficiency.
As the configuration of a waste ink tank for such ink as described above, the Applicant of the present application has proposed such a waste ink tank structure shown in FIG. 5 for the purpose of improving the absorbing efficiency and absorbing speed of waste ink.
A waste ink tank 100 stores an absorber 110 in a waste ink tank vessel 101. The absorber 110 has a characteristic that the horizontal absorbing speed is higher than the vertical absorbing speed, and has a through hole 103 extending from a top surface to a bottom surface thereof. The waste ink is led from a waste ink pipe 105 into a lower portion of the waste ink tank 100 through the through hole 103 and absorbed from the center in the horizontal direction, and this process is conducted step by step upward from below so as to be successively absorbed and held.
Even with the foregoing proposed structure, a water content may not be efficiently absorbed into the absorber in accordance with the ink composition and the environment where a recording apparatus is provided. For example, in the case of using ink having a high evaporation rate or when the environment is high in temperature and low in humidity, evaporation of a water content is promoted from a surface of the ink contacting with air so that a surface film which is a phenomenon peculiar to the pigment and resin dispersing type ink is formed on the ink surface. Newly stored waste ink is prevented from entering the absorber deeply because of formation of such a surface film. Thus, the waste ink cannot be absorbed efficiently.
Further, the residual solid component stays on the absorber surface in the form of a surface film although a water content is absorbed in the absorber, so that the ink evaporation rate in the surface film is considerably reduced. A solid component is accumulated on the absorber surface whenever waste ink is generated. In the case where waste ink is generated at a high frequency, however, additional waste ink is stored in the waste ink tank before the ink in the surface film is perfectly dried and solidified, so that the thickened ink which is not perfectly dried is further prevented from being dried. When the waste ink tank in the foregoing state is left in the environment which is high in temperature and high in humidity, a problem is caused so that the surface film is softened and the ink which is not perfectly dried absorbs humidity and fluidity is generated in the waste ink, resulting in leakage of ink during transportation.